1. Field of the Invention
The invention relates in general to protected electrical inductive apparatus, and more specifically to liquid-filled pad-mounted electrical distribution transformers having a dry well fuse assembly sealingly mounted through a wall portion of the casing, separate from the electrical bushings.
2. Description of the Prior Art
Protective fuses, such as full range current limiting fuses are used to protect liquid-filled pad-mounted electrical distribution transformers by interrupting fault current flow before peak current is reached. To facilitate fuse replacement without breaking the casing seal, the current limiting fuse may be mounted in a dry well fuse holder which is sealingly disposed through an opening in the casing such that the two electrical terminals or connections to the fuse holder are immersed in the liquid dielectric. The two electrical terminals include portions accessible from within the air space of the dry well fuse holder, and they are configured such that they automatically make electrical contact with the electrical contact portions of the associated removable fuse assembly. The inner portion of one of the electrical terminals is necessarily closer to the grounded metallic casing of the inductive apparatus than the other terminal, and high electrical stresses exist between this terminal and the grounded casing. Ionization of the air within the dry well fuse holder must be prevented, as a flashover may occur along the inside wall of the fuse holder, from the electrical terminal to the grounded casing. With the increasingly higher operating voltages, BIL ratings, and BIL withstand requirements, the spacing between the closest terminal and the casing must be increased, which deleteriously affects the size and thus the cost of the pad-mounted transformer.